The present invention relates to a method and apparatus for the production of staple cut fibers and more particularly to the method and apparatus for cutting tows of endless filament fibers to produce cut fibers of predetermined lengths which can be subsequently made into sliver.
It is well known to produce staple fibers by cutting a tow of filament fibers with a rotating knife that creates a pulling cutting effect. One such device is disclosed in German Pat. No. 964,213 which discloses two sets of endless conveyor belts, each set of which includes a pair of belts that touch each other. The two sets of belts are positioned on opposite sides of a cutting area. Between adjacent guide rollers of the sets of conveyor belts is a guiding slot. The tow of fibers is spread in an arcuate fashion and fed to the cutting area so that rotating circular knives can cut the endless fibers into predetermined lengths as the fibers move through the guiding slot. During the cutting operation the tow of fibers are held by the guide rollers of the feeding and removing conveyors. In such an apparatus however, the free ends of the cut endless fibers have to be moved ahead by the conveyors and guided into the grip of the guide rollers since the continuity of the fibers have been interrupted by the cut. This cannot be achieved very satisfactorily since the flexible fiber ends are free and tend to move to the side when they hit the guide rollers of the removing conveyors. As a result, the parallel alignment of the fibers is interfered with since a large amount of fiber ends are not being held by the guide rollers of the removing conveyors. Therefore, a precise and good quality sliver of uniform length fibers cannot be achieved.
In another device, such as disclosed in German Pat. No. 928,119 a continuously moving fiber tow is placed in a circumferential groove of a rotating wheel and guided in it to a cutting area. At the cutting area a rotating knife passes through radial slots provided in the rotating wheel for cutting the tow of fibers which is being held in place on the wheel before and after the cutting area by steel fingers. This apparatus however, has one drawback in that the fibers fall freely from the wheel after cutting and their partial alignment and orientation is lost.
Still another device for cutting a tow of endless fibers is disclosed in German Pat. No. 683,113. In this device a needle bed is positioned between a pair of feeding cylinders and a pair of removing cylinders. The tow of fibers passes between the needles in the needle bed and is cut by a cutting disc that moves transversely of the direction of the tow so that each is a reflected image of the preceeding cut. One disadvantage of such a device is that the cutting takes place between the feeding cylinders and the needle bed which tends to interfere with the parallel alignment of the fibers.
Another problem is that only cut fibers can be produced that are longer than the distance between the pairs of feeding cylinders and the needle bed since only then is a necessary support provided for the fiber filament.
The cutting through spaces between the needles of the needle bed has the advantage that the tow of filament fibers is being forced to stay between the pair of feeding cylinders and the needle bed and therefore staples of shorter lengths can be cut. The disadvantage of the uncontrolled freedom of movement of the cut fibers between the needle bed and the pair of removing cylinders remains however with this device especially with short fibers, and therefore an even fiber sliver cannot be produced. In addition, the material has an unsteady support on the needle bed since the needles of the needle rods have to be spaced apart to allow the knife to cut through the spaces between the needles. Since the knife has contact with the needle rod body while the filament fibers lying on the same are being cut, an overall unsatisfactory cutting quality results and the possibility of damaging the knife and the needle rod body arises.